1. Field
The present embodiment relates to information processing apparatuses which can play content, and particularly to an information processing apparatus which can play content distributed through a network.
2. Description of the Related Art
Digital broadcasting, which broadcasts digitally encoded content, has begun spreading in recent years. Digital broadcasting has a higher communication efficiency than analog broadcasting and can distribute high-quality content even in a limited communication band. In addition, it is easy to perform a variety of information processing on the content.
On the other hand, because a reproduction of digital content will not lower the quality, the protection of digital content is more important than the protection of analog content. Accordingly, much digital content is encrypted, and television sets supporting digital broadcasting incorporate a circuit for performing decryption processing. Personal computers (PCs) supporting digital broadcasting incorporate hardware including a television tuner and a circuit for performing decryption processing (refer to Japanese Unexamined Patent Application Publication No. 2003-198527).
From the viewpoint of convenience and flexibility in viewing content, content distribution through a network is expected, besides broadcasting. Distribution through a network will make it easy for the user to view content when he or she wants it (on-demand distribution). Moreover, it will be easy to distribute different content according to the user (refer to Japanese Unexamined Patent Application Publication No. 2004-54913).
In comparison with broadcasting, content distribution through a network has not yet come into wide use. A general apparatus for playing content distributed through a network is a PC, but it is difficult for the PC to combine content protection with user's convenience. As a general-purpose information processing apparatus, the PC cannot eliminate a possibility that content is used without authorization beyond the approved range by software tampered with. A PC equipped with specialized hardware to play content (refer to Japanese Unexamined Patent Application Publication No. 2003-158514) cannot support a variety of types of content with flexibility, wasting the versatility of the PC.
Currently under development is such a technology that allows content to be played by software, taking content protection into consideration, just by adding minimum hardware to the PC. For instance, one known technology uses hardware that continuously checks whether software being used to play content is authorized software distributed by a distributor (refer to Japanese Unexamined Patent Application Publication No. 2004-129227). The hardware should have such a characteristic that internally stored content cannot be referenced or updated from the outside (tamper resistance). This makes it possible to block unauthorized use of content by software tampered with and to achieve both content protection and user convenience.
The technology disclosed in Japanese Unexamined Patent Application Publication No. 2003-158514 can protect content from unauthorized use by software tampered with but cannot eliminate a possibility that the processing for playing encrypted content is analyzed. Because a software program for playing content is expanded on memory during playback, a user-created program can monitor the operation and can analyze the processing. If a decryption key or a decryption algorithm for use in content decryption is analyzed, content would be freely decrypted and used by the user.